The term shield as applied to radiation is defined as any material used to reduce the amount of radiation reaching one region of space from another region of space. An electrostatic shield when made of a series of parallel wires connected at one end and grounded from a common point is generally referred to as a Faraday shield or screen. One embodiment of an electrostatic shield which is also termed a Faraday shield is constructed of a series of parallel wires connected at one end like a comb. The common point is grounded. This structure of a Faraday shield provides electrostatic shielding while passing electromagnetic waves.
Present day shielding requirements in view of the use of the selected portions of the spectra in optical signalling and communication necessitates shielding from electromagnetic fields without shielding from the optical spectrum. Optical communication (opcom) is communication over relatively short distances by means of beams of visible, infrared, or ultraviolet radiation, or over much longer distances with laser beams.
Thus, there are some instances when optical information is being transmitted to an optically sensitive detector which is in an environment where the electromagnetic field strength around the detector is too great for the detector to function properly. In these instances the detectors must be shielded from the electromagnetic radiation. The typical shielding techniques involve building a Faraday cage shield out of conducting material. However, conducting materials are typically opaque to any optical signal. Therefore, in order to protect an optically sensitive detector from strong electromagnetic fields, the optical signal would also be shielded from the detector.
A primary object of this invention is to provide a shield structure which is an effective shield for electromagnetic fields without shielding the desired optical spectrum.
A further object of this invention is to provide a shield structure which employs optical thin film technologies while utilizing the Faraday cage effect for shielding a device from electromagnetic fields without shielding the device from the desired optical spectrum.
Still a further object of this invention is to provide an optically transmissive shield which is opaque to lower frequency signals.